Support is requested for a program of research in the developmental origins of motor control in humans. The overall goal of the program is an understanding of aspects of the motivational, neural, and biomechanic contributions to the acquisition of motor competence during the first year. A new model is proposed which integrates current theoretical advances in motor control with a developomental and ecological perspective. The model is used to conceptualize research in three areas. The first study is a completion and replication of a longitudinal investigation of the electromyographic and kinematic characterictics of spontaneous infant kicking, a behavior I believe is an important precursor to mature locomotion. This descriptive project will report on the temporal and topographical changes in leg movements, and the patterns of their underlying muscle activations. A second study asks what happens to a spontaneous movement when it comes under voluntary conrol. These experimens will reinforce spontaneous leg kicks for frequency and/or topographical qualities to assess which parameters are stable and which amenable to voluntary control. The third group of experiments will manipulate themass of the legs through adding weights and having infants move underwater. These studies will assess the effect of mass changes on movement quality. Infant motor behavior is a neglected area of study in human development and this research is unique in approaching motor development from the perspective of current motor theory. It offers the promise of leading to a new synthetic theory of motor development, but it also is an essential precursor to similar studies directed to diagnosis and treatment of neuromuscular dysfunctions and to the motor consequences of developmental delays.